With constant evolution of a wireless cellular network, orthogonal multiple access technologies widely applied to the third-generation (3G) and the fourth-generation (4G) mobile communications systems, such as a Code Division Multiple Access (CDMA) technology and an orthogonal frequency division multiple access (OFDMA) technology, are gradually unable to meet people's ever-increasing capacity requirement for the cellular network, such as massive access and constant improvement of spectral efficiency. In addition, the study and application of a non-orthogonal multiple access technology has been gradually attracting more attentions from the industry and academia. People expect that a future wireless cellular network, for example, the fifth-generation (5G) mobile communications system, can effectively increase a capacity by using the non-orthogonal multiple access technology.
A low-density signature (LDS) technology is a typical non-orthogonal multiple access and transmission technology. Certainly, the LDS technology may have another name in the communications field. This technology is used to superpose M (where M is an integer not less than 1) data streams from one or more users onto N (where N is an integer not less than 1) subcarriers for transmission, where data of each data stream is spread on the N subcarriers by means of sparse spread spectrum. When a value of M is greater than that of N, this technology can effectively increase a network capacity, including a quantity of accessible users of a system and spectral efficiency. Therefore, as an important non-orthogonal multiple access technology, the LDS technology has drawn more attentions, and become an important candidate access technology for future wireless cellular network evolution.
In a non-orthogonal multiple access system such as an LDS system, when a terminal device transmits an uplink data stream by using the non-orthogonal multiple access technology, the terminal device needs to know data transmission information such as a modulation constellation that is used to transmit the uplink data stream. However, selection and allocation of the data transmission information is usually completed by a network device, and the terminal device does not directly participate in this process. Therefore, after the network device allocates data transmission information such as a modulation constellation for a to-be-transmitted data stream of the terminal device, how to notify the allocated data transmission information to the terminal device is a technical problem to be urgently resolved.